The present invention relates to an apparatus for mixing and advancing a polymer melt.
In the processing of a thermoplastic material, the material is initially melted, for example, by an extruder and supplied as a polymer melt to further processing operations. To this end, the polymer melt is advanced by means of a conveying device. For further processing the polymer melt, the homogeneity of the melt constitutes an important criterion besides the dwelling time of the melt. To attain an adequately homogenized melt, the melt is therefore mixed by means of a mixer. In particular, in the case of high quality requirements when additives or fillers are incorporated, it is necessary to adapt to each other the melt throughput and the intensity of the mixing.
EP 0 636 190 and corresponding U.S. Pat. No. 5,637,331 disclose an apparatus, wherein the mixer is combined with a conveying device in one unit. In this unit, the mixing shaft of the mixer is driven together with the conveying device. In this connection, the rotational speed of the mixer is defined by the discharge of the conveying device, so that the mixing result is directly dependent on the conveying device. In the known apparatus, a main flow of the polymer melt is mixed in a mixing chamber by means of a rotating mixing shaft, and subsequently divided by means of the conveying device into partial flows, and advanced to a spinneret. In this connection, it is especially important that the partial flows be uniformly homogenized, for purposes of attaining a uniform product quality in the subsequent processing, in this instance in a spinning line.
U.S. Pat. No. 4,128,342 discloses an apparatus wherein the mixer shaft of the mixer is arranged at the end of an extrusion screw and driven by same. In this arrangement, the rotational speed of the mixer shaft is determined by the rotational speed of the conveying device, in this instance an extrusion screw.
Thus, in the known apparatus, the mixing result is dependent on the speed of the mixer shaft and the length of the mixing chamber. To obtain an intensive mixing at relatively low rotational speeds, it is necessary to construct the mixer chamber and thus the mixer shaft very long in the case of large throughput quantities.
It is accordingly an object of the invention to design and construct an apparatus of the initially described type in such a manner as to ensure, despite low rotational speeds of the mixer shaft, an intensive mixing of the polymer melt and with the mixer being constructed as compactly as possible.